A hard life can age you, literally, researchers say. In fact, children who are exposed to violence at a young age show changes in their DNA equivalent to several years of premature aging.

That’s the finding of an international group of scientists who analyzed data from the Environmental Risk Study (E-Risk), which tracked 2,232 children born between 1994 and 1995 in England and Wales. The researchers focused on 236 children whom they followed from age 5 to 10. Nearly half of the children had had some exposure to violence, either in the form of observing violent acts against their mother, being bullied themselves, or being the victim of aggressive acts by an adult.

The study’s lead author, Idan Shalev, in the department of psychology and neuroscience at Duke University, says that he and his colleagues were interested in seeing whether the long-term negative effect of violence on children’s later health and behavior might be related to the early aging of their cells. So they took DNA samples from each child at age 5 and again at age 10 and studied their telomeres, the repetitive sequence of DNA that caps chromosomes at each end. Over time, telomeres get shorter, since each time a cell divides, a bit of the telomere is lost. Once the telomeres reach a certain length, the cell starts to die, leading some experts to believe that telomeres are a master regulator, or chronological clock, that documents a cell’s aging.

In recent years, studies have shown that stress can whittle away at telomeres, aging cells before their time. Indeed, the current study showed that children who were exposed to two or more kinds of violence showed more erosion of their telomeres between ages 5 and 10 than those who led less stressful lives. What’s more, each of the types of violence Shalev and his group studied had an effect on shortening telomeres, but exposure to multiple types of violence had a cumulative effect.

“Children who experience violence appear to be aging at a faster rate,” Shalev said in a statement about the study, which was published in Molecular Psychiatry. “This finding suggests the importance of including telomeres as stress markers in research to evaluate the effects of stress.”

The study is the first to follow children and track changes to their DNA that might be related to their exposure to violence. Even after adjusting for other socioeconomic and physical factors that affect premature cell aging, such as poverty or obesity, the relationship remained. The study also adjusted for another important factor that previous studies were not able to account for — the natural variation in telomere lengths in individual people. By comparing the children’s telomere lengths at two different time periods, Shalev and his colleagues were able to avoid possible bias due to the fact that, for example, telomeres actually lengthen as they age in a small percentage of people. The comparison also allowed them to account for the fact that children exposed to violence tend to be less healthy as adolescents and adults, which could affect cell aging as well.

Shalev says that exposure to violence may be a form of stress that elevates oxidation and inflammation in the body, which are both processes that wear on cells and prompt them to divide faster and, therefore, age sooner. The fact that violence can be “seen” in a physical way in children’s cells, he says, “suggests new urgency for preventing harm to children.”

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.